The present invention relates generally to the art of mechanical power transmissions systems. More particularly, the present invention relates to a mechanical power transmission system having improved lubricant circulation apparatus.
Mechanical power transmission systems generally function to transmit mechanical power from a power source to a power consuming load. The speed or torque of the transmitted power may be varied as necessary or desirable to meet the exigencies of a particular application. For example, it is often desirable to control the degree of acceleration imparted to load by a prime mover, such as an electric motor. One transmission device utilized for this purpose is frequently referred to as a controlled start transmission. A controlled start transmission incorporates a multiple-disc clutch mechanism which may be selectively controlled as desired to regulate such acceleration.
An application in which controlled start transmissions are frequently employed is that of a belt conveyor system for transporting bulk materials. Conveyors of this type are frequently lengthy, and incorporate a plurality of drive motors spaced apart along their length. For example, it is not unusual for a belt conveyor utilized in a mining operation, such as coal or ore, to exceed a length of one mile or more. Generally, each of the drive motors spaced apart along the length of the conveyor would have a respective controlled start transmission associated therewith. In addition to controlling acceleration imparted to the belt conveyor during start up, these controlled start transmissions may be utilized during operation of the conveyor to effect substantially equivalent load sharing between each of the drive motors.
Mechanical devices such as controlled start transmissions, as well as ordinary speed reducers and other gear boxes, often generate a significant amount of heat during operation. This heat may be dissipated by circulating cooling fluid through an appropriate heat exchanger. Frequently, this cooling fluid may be the lubricant fluid also used to lubricate internal components of the particular mechanical device. Depending on the requirements of the particular application, the heat exchanger may be any one of several types, including a oil-air heat exchanger or a oil-water heat exchanger.
The lubricant fluid is circulated through the heat exchanger by an appropriate pump. Often, the lubricant fluid is pumped through the heat exchanger at a flow rate which, on a per minute basis, may exceed the capacity of the reservoir (or "sump") in which the lubricant fluid is maintained. For example, a flow rate exceeding 200 gallons per minute is not unusual in applications utilizing a controlled start transmission having a 50 gallon sump. In these applications, a centrifugal pump is generally preferred due the ability thereof to pump relatively large volumes of fluid without generating excessive pump noise levels.
In the past, the pumps utilized to produce such flow rates were often placed adjacent the heat exchanger in a location separate from the controlled start transmission itself. Additionally, these pumps were generally mounted such that the lubricant fluid was drawn into the pump impeller in a substantially horizontal direction. These prior art pumps, however, have been prone to several operational problems. For example, it was not unusual for these pumps to produce temporary discontinuities in flow of the lubricant fluid. Such temporary discontinuities have often been interpreted by electronic controllers as a system fault, thus leading to automatic shut down of the entire system, such as a belt conveyor system, with which the controlled start transmissions are being used. Additionally, internal seals within pumps have often failed more frequently than expected, thereby necessitating greater maintenance efforts than would otherwise be required.